Estimating products
The question
98 × 67
98×67
100×67
100×70
7000
- Do not work it out exactly. Round each number first. 98 is nearer 100 than 90, so to the nearest ten it becomes 100.
- 67 is nearer 70 than 60, so to the nearest ten it becomes 70.
- Now it is easy enough to do in your head: 100 × 70 = 7000.
- The exact answer is 6566, so the estimate of 7000 is 434 away. Close enough to catch a wrong answer with, and you did it in your head.
How it works.
- 01
Do not work it out exactly. Round each number first. 98 is nearer 100 than 90, so to the nearest ten it becomes 100.
- 02
67 is nearer 70 than 60, so to the nearest ten it becomes 70.
- 03
Now it is easy enough to do in your head: 100 × 70 = 7000.
- 04
The exact answer is 6566, so the estimate of 7000 is 434 away. Close enough to catch a wrong answer with, and you did it in your head.